Heretofore various methods of halftone reproductions have been utilized and examples of various different structures designed for halftone reproduction are disclosed in U.S. Pat. Nos. 532,326, 1,247,682, 1,289,129, 1,732,051, 2,123,830, 2,489,840, 2,703,281, 2,920,547, and 3,040,644.
However, these various structures have been specifically designed to perform specific functions not including the capturing of the range and contrast of reproduction materials to be copied, retarding the lighter gray from the white in black and white halftone negatatives and separating the gray-white contrast relation for printing purposes all in a single apparatus.
Some forms of previously known projection diaphragm structures have included means whereby the size of the aperture may be varied and also means for providing a plurality of apertures in predetermined pattern with the pattern of apertures rotatable about the center axis of the associated lens assembly. However, diaphragm structures for projection use constructed in a manner to provide both a variable size aperture of selected shape and the ability of the aperture formed to be angularly displaced about the center axis of the associated lens assembly and for the purpose of improving halftone reproduction and for color printing have not been heretofore provided.